L-Carnitine intake and high trimethylamine N-oxide plasma levels correlate with low aortic lesions in ApoE(-/-) transgenic mice expressing CETP.

OBJECTIVE: Dietary l-carnitine can be metabolized by intestinal microbiota to trimethylamine, which is absorbed by the gut and further oxidized to trimethylamine N-oxide (TMAO) in the liver. TMAO plasma levels have been associated with atherosclerosis development in ApoE(-/-) mice. To better understand the mechanisms behind this association, we conducted in vitro and in vivo studies looking at the effect of TMAO on different steps of atherosclerotic disease progression. METHODS: J774 mouse macrophage cells were used to evaluate the effect of TMAO on foam cell formation. Male ApoE(-/-) mice transfected with human cholesteryl ester transfer protein (hCETP) were fed l-carnitine and/or methimazole, a flavin monooxygenase 3 (FMO3) inhibitor that prevents the formation of TMAO. Following 12 week treatment, l-carnitine and TMAO plasma levels, aortic lesion development, and lipid profiles were determined. RESULTS: TMAO at concentrations up to 10-fold the Cmax reported in humans did not affect in vitro foam cell formation. In ApoE(-/-)mice expressing hCETP, high doses of l-carnitine resulted in a significant increase in plasma TMAO levels. Surprisingly, and independently from treatment group, TMAO levels inversely correlated with aortic lesion size in both aortic root and thoracic aorta. High TMAO levels were found to significantly correlate with smaller aortic lesion area. Plasma lipid and lipoprotein levels did not change with treatment nor with TMAO levels, suggesting that the observed effects on lesion area were independent from lipid changes. CONCLUSION: These findings suggest that TMAO slows aortic lesion formation in this mouse model and may have a protective effect against atherosclerosis development in humans.

Validation of theory of n-column separations with gas chromatograms predicted by commercial software.

A probability theory for the average number of compounds resolved by the partial separation of complex mixtures on n columns was tested using commercial-software predictions of gas chromatograms. Such n-column separations are traditional means for addressing peak overlap, in which one chooses additional columns of different selectivity to separate compounds that cannot be separated by a single column. Gas chromatograms of five types of complex mixtures containing from 99 to 283 compounds were predicted for eight stationary phases using both optimized and other temperature programs. The number n of columns for different mixtures varied from 2 to 5. The numbers of compounds separated as singlet peaks at different resolution thresholds were compared to predictions, as evaluated with point-process statistical-overlap theory based on a Poisson distribution. A good agreement between theory and results was found in all cases corresponding to low saturation. Both good and poor agreements were found for cases corresponding to high saturation. A good agreement also was found for results based on resolving complex mixtures by a single column subject to two temperature programs. The moments and distribution of the number of resolved compounds were computed by Monte Carlo simulation, thus gauging the significance of departures between results and theory. The potential of such simulations to explore the limitations of theory was briefly investigated.

Origin of peak asymmetry and isotherm nonlinearity in micellar electrokinetic chromatography: variation of peak shape with buffer concentration.

The diffuse fronts and sharp rears of peaks of nitrobenzene (nbz) solubilized at high concentrations in 50 mM SDS and 2.5, 25, and 50 mM sodium tetraborate buffers were modeled in MEKC by measurements of, and fits to, concave upward isotherms, and by numerical solution of the continuity equation. The isotherms varied with buffer concentration, with the smallest limiting slope and largest curvature found for the 50 mM tetraborate buffer. The Brunauer, Emmett, and Teller isotherm described the peak profiles in all buffers, with symmetrical peaks observed at sub- and low-mM levels of nbz, anti-Langmuirian peaks observed at 10-20 mM levels, and aquiline peaks resembling curved noses observed at 20-30 mM levels. The variation of the partition coefficient with nbz and buffer concentrations was shown to result from nonideal thermodynamics. High-buffer concentrations salt out nbz from the mobile phase, as quantified by a mobile-phase activity coefficient related to the Setchenov constant of nbz in sodium tetraborate. The activity coefficient of nbz in SDS micelles was shown to resemble that measured by other researchers for benzene in micelles of sodium octyl sulfate, i.e. it decreases with increasing solute concentration and increases with electrolyte concentration. Many examples from the literature are discussed, in which the variation of the intramicellar activity coefficient with solute mole fraction is consistent with peaks having diffuse fronts and sharp rears.

Modeling of anti-Langmuirian peaks in micellar electrokinetic chromatography: benzene and naphthalene.

Peaks of benzene (bz) and naphthalene (np) having diffuse fronts and steep rears under overload conditions were studied quantitatively in MEKC with SDS surfactant. The retardation factors of these compounds, solubilized at microM to mM concentrations by either 10, 30, or 50 mM SDS, were determined by vacancy MEKC and frontal analysis MEKC. Isotherm coordinates were calculated from the retardation factors, and the equation for the concave upward anti-Langmuir isotherm was fit to them. Peak profiles were computed with the MacCormack algorithm from the isotherm fits and a simplified continuity equation appropriate to MEKC. These profiles were compared to ones generated in normal MEKC from samples of bz and np solubilized at muM to mM concentrations by either 10, 30, or 50 mM SDS. In all cases, the anti-Langmuir isotherm described the asymmetry of experimental peaks. For bz in 30 and 50 mM SDS and np in 10 and 50 mM SDS, good to excellent agreement was found between the experimental and predicted profiles. For bz in 10 mM SDS, the experimental profiles were more broadened than the predicted ones, although their asymmetries agreed. For np in 30 mM SDS, the experimental isotherm predicted greater peak asymmetry than was observed, and the correct anti-Langmuir isotherm for all sample concentrations and field strengths was calculated from the most asymmetrical peak by the inverse method. The relative decrease of zone velocity with increasing analyte concentration was calculated from the isotherm parameters, electrokinetic mobilities, retardation factors, surfactant concentrations, and CMC. The simplification of the continuity equation was justified.